Electrical conduction of (NH3)(x)NaRb2C60

We investigated the electrical conductivity of alkali fullerides K3C60 and (NH3)(x)NaRb2C60 by the microwave cavity perturbation method. We found that the resistivity of (NH3)(x)NaRb2C60 is rather metallic both for x = 0.8 an d x = 0.9. These results suggest that the disappearance of superconductivit y in (NH3)K3C60 is due to the distortion of the crystal structure from the cubic structure. This also suggests that superconductivity of alkali-doped fullerides can appear only in the cubic structure. (C) 2001 Elsevier Scienc e B.V.. All rights reserved.